Ganalyzer: A Tool for Automatic Galaxy Image Analysis

Shamir, Lior

doi:10.1088/0004-637x/736/2/141

Cited by 74 publications

(159 citation statements)

References 27 publications

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“…The handedness of each spiral galaxy was determined by transformation of the images to their radial intensity plots, as done by the Ganalyzer method [5,6].…”

Section: Image Analysis Methodsmentioning

confidence: 99%

“…To avoid possible human bias, another dataset that was used in the experiment was the SpecObj view of SDSS DR7, which is based on the SpecObjAll table, but excludes bad and duplicate data. The galaxies in the SpecObj view were classified automatically using the Ganalyzer method [5], providing a dataset of 345,599 spiral galaxies that are not edge-on. Declination of the galaxies was between ∼-11.…”

Section: Image Datasetmentioning

confidence: 99%

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Handedness asymmetry of spiral galaxies with z<0.3 shows cosmic parity violation and a dipole axis

Shamir

2012

Physics Letters B

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A dataset of 126,501 spiral galaxies taken from Sloan Digital Sky Survey was used to analyze the largescale galaxy handedness in different regions of the local universe. The analysis was automated by using a transformation of the galaxy images to their radial intensity plots, which allows automatic analysis of the galaxy spin and can therefore be used to analyze a large galaxy dataset. The results show that the local universe (z<0.3) is not isotropic in terms of galaxy spin, with probability P <∼ 5.8 · 10−6 of such asymmetry to occur by chance. The handedness asymmetries exhibit an approximate cosine dependence, and the most likely dipole axis was found at RA=132o , DEC=32 o with 1σ error range of 107 o to 179 o for the RA. The probability of such axis to occur by chance is P < 1.95 · 10 −5 . The amplitude of the handedness asymmetry reported in this paper is generally in agreement with Longo, but the statistical significance is improved by a factor of 40, and the direction of the axis disagrees somewhat.

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“…The handedness of each spiral galaxy was determined by transformation of the images to their radial intensity plots, as done by the Ganalyzer method [5,6].…”

Section: Image Analysis Methodsmentioning

confidence: 99%

Section: Image Datasetmentioning

confidence: 99%

Handedness asymmetry of spiral galaxies with z<0.3 shows cosmic parity violation and a dipole axis

Shamir

2012

Physics Letters B

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“…Linear regression is applied across the vertical lines of the radial intensity plot for each group of peaks, and the sign of the slopes reflect the direction of the arm, therefore determining the handedness of the galaxy. The algorithm is described in details and numerous examples in (Shamir 2011b;Hoehn & Shamir 2014;Shamir 2012), and the process of galaxy classification is described in (Shamir 2016).…”

Section: Datamentioning

confidence: 99%

Photometric Asymmetry Between Clockwise and Counterclockwise Spiral Galaxies in SDSS

Shamir

2017

Publ. Astron. Soc. Aust.

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While galaxies with clockwise and counterclockwise handedness are visually different, they are expected to be symmetric in all of their other characteristics. Previous experiments using both manual analysis and machine vision have shown that the handedness of Sloan Digital Sky Survey (SDSS) galaxies can be predicted with accuracy significantly higher than mere chance using its photometric data alone, showing that the photometric pipeline of SDSS is sensitive to the handedness of the galaxy. However, some of these previous experiments were based on manually classified galaxies, and the results may therefore be subjected to bias originated from the human perception. This paper describes an experiment based on a set of 162,514 celestial objects classified as clockwise and counterclockwise spiral galaxies in a fully automatic process, showing that the source of the asymmetry in SDSS database is not the human perception bias. The results are compared to two smaller datasets, and confirm the observation that the handedness of galaxies in SDSS database can be predicted by the way SDSS measures their photometry, and show that the position angle of counterclockwise galaxies computed by SDSS photometry pipeline is consistently higher than the position angle computed for galaxies with clockwise patterns. The experiment also shows statistically significant differences in the measured magnitude of SDSS galaxies, according which galaxies with clockwise patterns imaged by SDSS are brighter than galaxies with counterclockwise patterns. The magnitude of that difference changes across RA ranges, and exhibits a strong correlation with the cosine of the right ascension.

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“…In addition, tools to automate the processing of large data sets to calculate these structural parameters such as Galapagos (Barden et al 2012) and it's multi-band variant produced by the MegaMorph project (Häußler et al 2013). Other tools use image processing techniques such as Ganalyzer and SpArcFiRe (Shamir 2011;Davis & Hayes 2014). In recent years, machine learning has once again become a prominent area of research following high-profile advances in object recognition, image classification and generative models (Goodfellow et al 2014;He et al 2016;Redmon et al 2016).…”

Section: Introductionmentioning

confidence: 99%